Upgrading project from 4.27 to 5.3 breaks root motion animations?

hi I’ve upgraded a project from 4.27 to 5.3 and my root motion anims now skate around all over the place - looks like the rotations are screwed They were fine in 4.27. A

Any ideas?

I have reimported the amins from source files to see what’s going on.
In Animation Viewer the root is rotating and translating correctly (with Root Motion off). When it’s in an Anim Blueprint it’s fine with the Root Motion off. When Root Motion is on it become wonky as if the rotations are backwards or something. Ive got both engine version of the project open to do a side by side comparison of settings and they seem the same.

Also this may or may not be connected - the skeletal mesh seems to have lost various polys or rather has been converted to a low poly version. Reimporting the skel mesh fixes this -or I have discovered that setting the Percentage of Triangles to 1.0 seems to fix it. (my characters don’t have LOD)